摘要:

In this investigation, the coefficients of thermal expansion of a number of crystals belonging to two structure types rutile and calcite have been studied by the x‐ray method with a view to correlating thermal expansion with crystal structure. The crystals studied areMgF2,ZnF2,NiF2,MnF2,CoF2,FeF2,SnO2,PbO2,TiO2(rutile),CrO2andRuO2belonging to the rutile type andCaCO3(calcite),CdCO3,ZnCO3,MgCO3,ScBO3andNaNO3belonging to the calcite type. The coefficients of thermal expansion have been evaluated from the precision lattice parameters determined with a Unicam 19 cm high temperature powder camera in the temperature range 30°C to 700°C. An attempt is made to correlate the variation in the coefficients of thermal expansion from crystal to crystal with the bond type, the interionic distances and the electronic configuration of the ions in the case of the rutile type compounds and with the ionic charge and the anion cation distance in the case of the calcite type compounds.

ISSN:0094-243X    

DOI:10.1063/1.2945925

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The thermal expansion behavior of unidirectional fiber composites may be predicted by the use of a discrete element method of analysis. A representative “cell” is selected and subdivided into triangular elements. Matrix equations relating the forces and displacements at each vertix with allowance for thermal expansion, together with equilibrium, compatibility and boundary conditions provide the longitudinal and transverse thermal expansion coefficients. The anisotropy in the thermal expansion and elastic behavior of the fibers is taken into account. The method is applied to boron‐aluminum composites of hexagonal and square array of fibers, and served to check the accuracy of computations. It is found that a cell of 58 nodes and 90 elements is adequate. Applied to hexagonal array graphite‐epoxy composites, the method was used to examine the effects of the fiber volume fraction and fiber elastic constants on the expansion behavior. It is found that both longitudinal and transverse coefficients deviate greatly from the rule of mixture's values. Poisson's ratios of the fiber and its transverse Young's modulus are found to have very little effect on the thermal expansion behavior of the composite.

ISSN:0094-243X    

DOI:10.1063/1.2945927

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The objective of the investigation was to determine the cause of wide variations (factor of 5) observed in the bulk thermal expansion of the polycrystalline graphites: ATJ‐S, AXF‐5Q, mesophase and isostatically pressed. An attempt to rationalize this spectrum on the basis of lattice thermal expansion was unsuccessful because of the relatively small differences in that lattice expansion. Addition of boron to the isostatically pressed graphite reduced the thermal expansion in the c‐direction by approximately 30%. The very low thermal expansion coefficient of ATJ‐S as compared to AXF‐5Q and the mesophase‐based graphite can be explained by the existence of very small microcracks between the layer planes in the ATJ‐S filler particles. In the AXF‐5Q and mesophase‐based graphites, very little micro‐cracking could be distinguished. The qualitative theory of Mrozowski and the more quantitative model of Buessem were examined. It was found that the results are essentially in agreement with Buessem's model. The isostatically pressed material must possess significant tessellated stresses or distortion in order to explain the very high bulk expansion.

ISSN:0094-243X    

DOI:10.1063/1.2945928

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Thermal expansion, specific heat, and ultrasonic data are presented for several metals, alloys, ceramics, and polymers, in order to define the magnitude of energy changes which occur when the materials are heated or cooled. Thermal Gruneisen ratios were computed as a function of temperature and numerous ultrasonic and thermodynamic equations were derived from the thermal data combined with measured compressibility data. Attempts to relate the volume coefficient of expansion, &bgr;, to heat capacity at constant volume, Cv, and to the elastic properties of polymers are discussed. Correlations are made between the measured thermal Gruneisen coefficients and those obtained from the change of atomic vibrational frequency with the change of volume as defined ultrasonically.

ISSN:0094-243X    

DOI:10.1063/1.2945929

出版商:AIP    

年代:1974

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.2945930

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A program is described for measurement of dimensional stability of fused silica and several ultralow thermal expansion materials. Two techniques are being used: Fizeau interferometry by NBS‐Corning and Fabry‐Perot interferometry by the Optical Sciences Center, University of Arizona. In the latter measurements an accuracy of one part in 109is sought. A by‐product of the Arizona results will be measurements of the stability of optical phase shifts on reflection from multilayer stacks and also dimensional stability of optical contacts.

ISSN:0094-243X    

DOI:10.1063/1.2945931

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The equation of state and thermal expansion of rubidium bromide have been studied on the basis of the simple shell model taking the electronic polarisabilities of both the ions into account. The static pressure has been evaluated from the Coulomb interaction supplemented by a repulsive potential of the Born‐Mayer type. The thermal pressure has been calculated from the vibration spectrum of the lattice. Out of the seven parameters of the model three, namely, the ionic and shell charges have been assumed to be volume independent although the individual values of these vary with volume. The vibration frequencies have been computed for a one thousand‐point mesh in the Brillouin zone at eleven closely spaced volumes. The total pressure has been obtained by adding the static and thermal pressures. The isotherms have been drawn in the temperature range 0 to 950 K, whose intercepts on the zero‐pressure axis give the thermal expansion coefficients. In agreement with Herzfeld and Mayer's theory the isotherm at 950 K, which is the melting point of this salt, has a minimum on the zero pressure axis. The calculated thermal expansion coefficients are in satisfactory agreement with the measured values of James and Yates and of Deshpande and Sirdeshmukh.

ISSN:0094-243X    

DOI:10.1063/1.2945932

出版商:AIP    

年代:1974

数据来源: AIP